A device of this type has become known from U.S. Pat. No. 3,420,232. Saturated anesthetic vapor from an evaporator chamber is mixed with the anesthetic gas via a dispensing means in the anesthetic vaporizer operating according to the bypass principle in order to set a predetermined concentration of anesthetic in the anesthetic gas. The anesthetic vaporizer is provided with a shut-off valve, which is designed to shut off the gas flow from the evaporator chamber in a first switching position, so that the anesthetic gas reaches a gas outlet from a gas inlet via a bypass line. In a second switching position, the gas flow is released via the evaporator chamber and anesthetic vapor can be mixed with the anesthetic gas with the dispensing device. The shut-off valve comprises a lower part provided with gas ducts, which is part of the evaporator housing, and a rotatably movable upper part, which is fastened thereto in a rotatingly movable manner and has kidney-shaped gas ducts. Depending on the angular position of the upper part, the kidney-shaped gas ducts of the upper part connect corresponding gas ducts in the lower part, so that a gas flow is released via the shut-off valve or the gas ducts in the lower part are closed. The upper part has a carrier pin, which is connected with the setting member for the anesthetic concentration. The shut-off valve is closed in the zero position of the setting member and the anesthetic gas flows via the bypass line directly from the gas inlet to the gas outlet. If the setting member is set to a certain anesthetic concentration starting from the zero position, the shut-off valve opens above the carrier pin and the gas flow from the evaporator chamber is released.
An anesthetic vaporizer, in which it is possible to switch over between a transport position, a zero position and a dispensing position by means of individual valves, which are actuated by the setting member, is known from DE 196 13 754 C1 (corresponding to U.S. Pat. No. 5,671,729). The evaporator chamber is completely closed in the transport position of the setting member, so that neither liquid nor gaseous anesthetic can escape. A ventilating valve, with which the pressure in the evaporator chamber of the anesthetic vaporizer can be released, is opened during the transition from the transport position into the zero position. The ventilating valve is again closed during the transition of the setting member into the dispensing position, so that the anesthetic can be dispensed at the pressure level prevailing during operation.
A certain system pressure must be maintained within the anesthetic tank in case of anesthetics with a low boiling pint in order to prevent the anesthetic from boiling. A pressure control circuit with a differential pressure sensor as well as a dispensing valve is usually used for the dispensing branch in such evaporators. The differential pressure sensor is especially sensitive to high pressure amplitudes and pressure shocks even if these reach the differential pressure diaphragm with an offset in time.
However, an increase in pressure within the anesthetic vaporizer may also be due to external causes, for example, a kinked supply tube for anesthetic gas, which is to be enriched with anesthetic vapor. Such pressure shocks may occur with the anesthetic vaporizer switched on and with the anesthetic vaporizer switched off.
In addition, a pressure build-up, which may damage delicate measuring systems, may occur due to minor leaks at dispensing components within the dispensing device when the anesthetic vaporizer is switched off when the anesthetic gas is sent past the dispensing device directly into the anesthesia apparatus. Even though it would be possible to protect these measuring systems with a separate pressure limiting valve, additional components are necessary for this.